#include <bits/stdc++.h>
using namespace std;

string plus26(string a, string b){ // 需要保证a比b长
    string res;
    int alen = a.size(), blen = b.size();
    int carry = 0;
    for(int i = 0; i < blen; ++i){
        int anum = a[alen - i - 1] - 'a', bnum = b[blen - i - 1] - 'a';
        int plus = anum + bnum + carry;
        carry = plus / 26;
        plus = plus % 26;
        res += (char)('a' + plus);
    }

    if(alen > blen){
        int apos = alen - blen - 1;
        while(apos >= 0){
            int anum = (a[apos] - 'a') + carry;
            carry = anum / 26;
            anum = anum % 26;
            res += (char)('a' + anum);
            apos--;
        }
    }
    while(carry != 0) {
        int up = carry / 26;
        carry = carry % 26;
        res += (char)('a' + carry);
        carry = up;
    }

    reverse(res.begin(), res.end());
    return res;
}

int main(){
    int n;
    cin >> n;
    while(n--){
        string a, b;
        cin >> a >> b;
        if(a.size() < b.size()){
            string tmp = a;
            a = b;
            b = tmp;
        }
        cout << plus26(a, b) << endl;
    }
    system("pause");

}